Hermetic electronic equipment with flexible diaphragm, fastened to case by elastic U-shaped ring, for absorbing pressure fluctuations

ABSTRACT

An electronic circuit equipment including a substantially box-shaped case main body (10) for defining a sealed interior space therein and an electronic circuit board (11) having a plurality of electronic components (12) thereon. The case main body (10) comprises a case body (13) and a flat plate-shaped lid (17) positioned properly with respect to the case body (13) to seal the interior space. A vent hole (20) is formed in the bottom wall of the case body (13) for communicating the interior of the case body (13) with ambient atmosphere. A cover member is attached to the case body (13) to cover the vent hole hermetically. By using a cover member, the interior space of the case body (13) is sealed for protecting electronic components (12) on the electronic circuit board (11) from moisture and rainwater and, for absorbing a pressure fluctuation therein. A mounting flange extends from the case body and surrounds the vent hole. The cover member is a flexible diaphragm with a circumferential bulge. The flexible diaphragm is fastened to the mounting flange by a press-fit elastic U-shaped ring which presses the circumferential bulge against the mounting flange so as to form a hermetic seal.

This is a continuation of application Ser. No. 08/124,857 filed Sep. 22,1993, now abandoned, which is a Continuation of application Ser. No.07/889,432, filed May 28, 1992, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a hermetic case for mounting a circuit boardand an electronic circuit apparatus using above hermetic case, for use,for example, in an automotive ignition timing control system of aninternal combustion engine.

FIG. 8 illustrates one example of a conventional electronic circuitapparatus for use in an automotive ignition timing control system. InFIG. 8, reference numeral 1 designates an electronic circuit boardhaving electronic components la thereon, 2 designates a case bodyincluding a case main body 2a mounting the circuit board 1 therein, 3designates a channel formed in a surrounding edge of the case main body2a, 4 designates a lid for covering the case main body 2a, 5 designatesa folded edge at a surrounding edge of the lid 4, and 6 designates anepoxy resin filler filled between the folding part 5 and the channel 3.

In order to prevent moisture in the ambient atmosphere from causing anyadverse effect on the electronic components 1a on the circuit board 1within the case body 2, the ease main body 2a and the lid 4 are made ofa plastic material and are hermetically sealed by the epoxy resin filler6. Also, the circuit board 1 is securely attached to the plastic mainbody 2 by means of screws 7.

In the electronic circuit apparatus as described above, pressure withinthe sealed case 2 changes with the temperature of the ambient atmospherechanges, which can range from -40° C. to 120° C. As this pressurefluctuation occurs repeatedly, the case 2 composed of the case main body2a and the lid 4 can to crack, and ambient moisture and rainwater canenter into the interior, of case 2 thereby damaging the electroniccomponents.

Also, because of the repeated pressure fluctuation, the case body 2 andthe electronic circuit board 1 are repeatedly deformed and bent. Thiscauses the solder connections between the circuit board 1 and theelectronic components 1a to be damaged.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide anelectronic circuit apparatus free from the above-discussed problems ofthe conventional electronic circuit apparatus.

Another object of the present invention is to provide an electroniccircuit apparatus in which the electronic components are protected frommoisture, and the pressure fluctuation of the sealed inner space of thecase body is absorbed.

A further object of the present invention is to provide an electroniccircuit apparatus in which the case body is kept from bending andcracking.

A still further object of the present invention is to provide anelectronic circuit apparatus in which the electronic circuit board iskept from flexure caused by the bending of the case body, and the solderconnections of the electronic components thereon are not broken.

With the above objects in view, the electronic circuit apparatus of thepresent invention comprises a case body which defines therein ahermetically sealed space for mounting electronic components. The casebody is provided with a vent hole and a moisture-impermeable flexiblecover member, which may be a diaphragm, for protecting the electroniccomponents from moisture and for absorbing pressure fluctuation.

By using the vent hole and the cover member, the pressure of the sealedinner space is kept constant. When the ambient temperature rises, thepressure of the sealed inner space start to increases. The diaphragmbends and the air in the space between the diaphragm and the cover comesout through the vent hole. The pressure inside the is kept case equal tothe pressure outside the case. The case body is kept from cracking andthe electronic circuit board never bends. Further, the diaphragm sealsthe vent hole hermetically, and moisture of the ambient atmosphere neverenters the sealed inner space and never touches the electroniccomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent from thefollowing detailed description of the preferred embodiments of thepresent invention, taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a longitudinal sectional view of an apparatus of theelectronic circuit apparatus of the present invention;

FIG. 2 is an enlarged fragmented sectional view of the cover meansillustrated in FIG. 1;

FIG. 3 is a top plan view of the diaphragm illustrated in FIG. 1;

FIG. 4 is a longitudinal sectional view of another embodiment of theelectronic circuit apparatus of the present invention;

FIG. 5 is an enlarged fragmented sectional view of the cover meansillustrated in FIG. 4;

FIG. 6 is a longitudinal sectional view of still another embodiment ofthe electronic circuit apparatus of the present invention;

FIG. 7 is a longitudinal sectional view of still another embodiment ofthe electronic circuit apparatus of the present invention;

FIG. 8 is a longitudinal sectional view of a conventional electroniccircuit apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an electronic circuit apparatus of the presentinvention, which comprises a substantially box-shaped plastic case mainbody 10 defining an interior space therein, and an electronic circuitboard 11 having a plurality of electronic components 12 thereon.

The case main body 10 comprises a case body 13 having a bottom wall 14which defines a bottom major surface wall of the case main body 10 andside walls 15 extending upwardly from the bottom wall 14. The side walls15 are provided at their top edges, which define an open end of the box,with channels 16 connected to each other to extend over the entirecircumference. The case main body 10 also comprises a substantially flatplate-shaped lid 17 having a continuous folded edge 18 extendingdownwardly. The folded edge 18 is inserted into and engages the channel16 formed in the case body 13, when it is placed on the case body 13 sothat the lid 17 is properly positioned with respect to the case body 13.In order to hermetically seal the joint between the folded edge 18 andthe channel 16, an epoxy resin filler 19 is filled in the channel 16.

The case body 13 further comprises a vent hole 20 formed in the bottomwall 14 of the case body 13 for communicating the interior space withinthe case main body 10 to the exterior of the case main body 10. The venthole 20 is surrounded by an annular mounting flange or mounting bed 21rising from the bottom wall 14 of the case body 13. The mounting bed 21has a top end surface 21a, from which an annular riser wall 22 along theouter circumferential surface of the mounting bed 21 extends. The venthole 20 is covered by a cover member such as a flexible diaphragm 23attached to the top end surface 21a of the mounting bed 21. Thediaphragm 23 is attached and sealed to the mounting bed 21 by means ofsuitable fastener such as a spring ring 24. Spring ring 24 has aU-shaped cross section and is elastically fitted against the top endsurface 21a and an inner circumferential surface 22a of the annularriser wall 22 on the mounting bed 21. The diaphragm 23, the shape ofwhich is substantially inverted dish-shaped, has a circumferential bulge25 at its edge which is inserted into and sealingly contacted with themounting bed 21 when the spring ring 24 is press-fit in place. Thus, theinterior space of the case body 13 is hermetically sealed, therebyprotecting the electronic components 12 from moisture and rainwater andabsorbing the pressure fluctuation of the sealed space. Since electroniccomponents 12 are mounted on one side of electronic circuit board 11 anddiaphragm 23 faces the opposite side of electronic circuit board 11,diaphragm 23 will never come in contact with electronic components 12.

FIG. 4 illustrates another embodiment of the electronic circuitapparatus of the present invention, which has basically the samestructure as that illustrated in FIG. 1 but is different in one aspect.Such different structure is a cover member to cover a vent hole 20. Thecover member comprises a balloon 26 attached and sealed to an annularmounting flange 28 which rises around the vent hole 20 from the bottomwall 14 of the case body 13 by means of suitable fastener such as anelastic spring ring 27, as illustrated the enlarged fragmented sectionalview in FIG. 5. The shape of the cover member can vary widely.

FIG. 6 illustrates still another embodiment of the electronic circuitapparatus of the present invention, which comprises a case body 30composed of substantially flat box-shaped separate sections 30a providedat their surrounding open end with brim 31. A vent hole 20 is formed inone of separate sections 30a, and a cover member for covering anelectronic circuit board 11 comprises a gas-impermeable flexible sheet32. The flexible sheet 32 wrapping the electronic circuit board 11 isinserted between the separate sections 30a, and is clamped at the brims31 by means of a suitable fastener such as screws 33 to seal theinterior space of the flexible sheet 32. The case body itself does notneed to be gas-impermeable and the assembling operation is easy.

FIG. 7 illustrates still another embodiment of the electronic circuitapparatus of the present invention, which has also basically the samestructure as that illustrated in FIG. 1. A case body 13a comprises twomajor surface walls 14 and 17, and side walls 15 extending between themajor surface walls 14 and 17. A vent hole 20 is formed in one of themajor surface wall 14 and a cover member such as a substantially flatflexible diaphragm 40 is attached to the top end surface 21a of anannular mounting flange 21 which is rising from the major surface wall14. A detailed fastening arrangement for attaching the flexiblediaphragm 40 is, for example, the same way as described in thedescription of FIG. 1. The flexible diaphragm 40 extends substantiallyalong and over the entire major surface wall 14. Since the area of theflexible diaphragm 40 is larger than that of the diaphragm 23 of FIG. 1,the flexible diaphragm 40 can be made more sensitive and attached atlower position, while the same volume needed for absorbing a pressurefluctuation in the sealed space of the case body 13a is maintained. Thecase body 13a can be miniaturized.

As above-mentioned, the electronic circuit apparatus of the presentinvention is watertight and, of course, can be used in an ignitiontiming control system of an outboard motor of a boat.

What is claimed is:
 1. A hermetic case for encasing an electroniccircuit board having an electronic element thereon comprising:a casebody defining a hermetically sealed space for encasing an electroniccircuit board; a vent hole disposed in said case body communicating saidsealed space with ambient atmosphere; and a freely flexible cover means,exclusively attached to said case body and not in contact with eitherthe electronic circuit board or the electronic element, for protectingthe electronic element from moisture and absorbing a pressurefluctuation of said sealed space to prevent flexure of the electroniccircuit board, wherein said cover means comprises: a mounting flangeextending from said case body and surrounding said vent hole; a flexiblediaphragm sealingly attached to said case body around said vent holehaving a circumferential bulge integrally formed at its edge sealinglycontacting said mounting flange to seal said vent hole, saidcircumferential bulge being an outcropping of said flexible diaphragm;and fastening means pressing said circumferential bulge of said flexiblediaphragm against said mounting flange to provide a hermetic sealtherebetween, said fastening means comprising an elastic ring having aU-shaped cross section which is press-fit onto said mounting flange,wherein the electronic element is exclusively mounted on a first side ofthe electronic circuit board, and said cover means faces a second sideof the electronic circuit board, opposite the first side, no otherelectronic elements being mounted on the second side of the electroniccircuit board.
 2. A hermetic case as claimed in claim 1, whereinsaidflexible diaphragm has said circumferential bulge if said flexiblediaphragm is in a free uncompressed state.
 3. An electronic circuitapparatus comprising:a case body defining a hermetically sealed spacetherein; a circuit board having an electronic element exclusivelymounted on a first side of said electronic circuit board, said circuitboard fixedly mounted to said case body in said sealed space; a venthole disposed in said case main body communicating said sealed spacewith ambient atmosphere; and a freely flexible cover means, exclusivelyattached to said case body and not in contact with said electronicelement, for protecting said electronic element from moisture andabsorbing a pressure fluctuation of said sealed space to prevent flexureof said circuit board, wherein said cover means comprises: a mountingflange extending from said case body and surrounding said vent hole; aflexible diaphragm sealingly attached to said case body around said venthole having a circumferential bulge integrally formed at its edgesealingly contacting said mounting flange to seal said vent hole saidcircumferential bulge being an outcropping of said flexible diaphragm;and fastening means pressing said circumferential bulge of said flexiblediaphragm against said mounting flange to provide a hermetic sealtherebetween, said fastening means comprising an elastic ring having aU-shaped cross section which is press-fit onto said mounting flange,said cover means facing a second side of said electronic circuit board,opposite said first side, no other electronic elements being mounted onthe second side of the electronic circuit board.
 4. An electroniccircuit apparatus as claimed in claim 3, whereinsaid flexible diaphragmhas said circumferential bulge if said flexible diaphragm is in a freeuncompressed state.
 5. An electronic circuit equipment as claimed inclaim 3, wherein said cover means are disposed inside of said case body.